Method of treating copper and copper alloys



INVENTOR. C/Z'Fence f. /r/017.

C. E. IRION METEOD 0F TREATING COPPER AND COPPER ALLOYS Filed NOV. 11, 1932 Jan. 9, 1934-.

Patented Jan. 9, 1934 UNITED STATES PATENT OFFICE METHOD OF TREATING COPPER AND COPPER ALLOYS Application November 11, 1932 Serial No. 642,251

18 Claims.

My invention relates to a method of treating copper and copper alloys. It pertains especially to the treatment of these materials so as to prevent tarnishing and to preserve the surfaces thereof from other deleterious influences.

In the prior art, attempts have been made to preserve the surfaces of metals. Some of these methods have involved the application of materials which modify the surface of the metal chemically and thus produce a preserving coating. One suggested method has involved the ap plication of insoluble cyanides electrolytically applied. Such a method, however, in experiments I have made produces a coating that is is rough and grainy, and which, when thick, has a dark color that hides the color of the copper, and when thin does not resist tarnish much better than uncoated copper.

One of the objects of my invention is to proto vide a method of protecting copper or its alloys so as to prevent tarnishing thereof.

Another object of my invention is to provide a method of protecting copper or its alloys by the application of such a coating thereto that .25 the natural color of the coated material will be preserved or, if modified, that this modified color ing only slightly alters the natural color and texture of the original material.

Another object of my invention is to provide 10 a method of protecting copper or its alloys by the application thereto of a coating which will be horny or smooth in texture.

Another object of this invention is to provide a method of protecting copper or its alloys by the chemical combination of a coatingtherewith and through the medium of comparatively inexpensive steps for the aflixing of this coating. Copper and its alloys, while highly resistant to corrosion by most substances, are tarnished 60' by the atmosphere in periods varying from a few days to a few months. This is especially true of pure copper and of copper alloys containing sufllcient copper to give a coppery or yellow color. In tarnishing, these materials are ordi- 15 narily darkened. Certain silvery colored copperalloys, especially those containing large amounts of nickel, may in the first stages of tarnish be dulled or "fogged, the tarnished product having a light color. The method to be described herein is especially valuable for preserving the appearance of the "coppery or yellow metals,

though it is applicable to these silvery alloys as well.

My invention contemplates the treatment of the clean metal surface with a water soluble salt of hydroferrocyanic acid. Potassium or sodium ferrocyanide is a suitable salt for this purpose. The solution may be applied by dipping, spraying, brushing or by other convenient means. The application of such a solution to the clean metal surface results in the formation on this surface of a film which is firmly adherent thereto, as a result of chemical combination, and which greatly increases the tarnish resistance. Moreover, the original color of the material is only slightly o5 changed by this treatment.

Though very satisfactory results are obtained by treating the clean metal surface with the water solutionof potassium or sodium ferrocyanide,,sti11 better results may be obtained by first adding a small amount of acid to the solution. For example, ii 0.1% of glacial acetic acid is added to a 1% water solution of potassium ferrocyanide and a piece of commercial copper is dipped in this solution for fifteen minutes, it will receive an adherent and tarnish resisting film. Solutions that contain a very small amount of hydroferrocyanic acid, such as is freed by a weak acid from a soluble salt of hydroferrocyanic acid, produce the film. This film will be even superior to that obtained by a similar water solution of potassium ferrocyanide. Tests have shown that this film will withstand an atmosphere containing 0.05% hydrogen sulphide of 40% relative humidity at 30 C. for over 100 minutes, whereas, clean untreated copper is distinctly tarnished by this atmosphere in about one minute.

One of the functions of the acetic acid is to reduce the alkalinity of the solution which results from the production of the copper ferrocyanide which forms the coating. This tendency towards neutralization of the alkali may result in the formation of potassium acetate. 0bviously, other acids than acetic acid, preferably weak acids, may be used to perform this function, though acetic acid is preferred.

Atmospheric tarnish results from the chemical action of the gases of the atmosphere. Sulphur dioxide and hydrogen sulphide, aided by the oxy- 10 7 gen of the air and water vapor, are the principal tarnishing agents. Hydrogen-sulphide generally predominates indoors, while sulphur dioxide appears to be more prevalent outdoors. Since it is well known that. for most substances, hydrogen lf sulphide is a more severe tarnishing agent than sulphur dioxide, there is every reason to believe that substances resistant to hydrogen sulphide will be more resistant to sulphur dioxide.

Under certain conditions my tarnlsh-r treatment results in-a surface with a better tarnish resistance than the ferrocyanide treatment alone will provide.

Use of sodium azide upon copper or copper alloys leads to a coloration of the surface, varying from a very light pink to a red. The intensity of this coloration depends largely upon the length of time the sodium azide is permitted to act. The sodium azide treatment produces a coating which appears to be especially active so that when the metal so treated is in turn subjected to the ferrocyanide bath, the coating produced by the ferrocyanide bath is more rapidly produced, and is even tougher and more adherent than when it is formed without the azide pretreatment. The coating produced by azide treatment followed by ferrocyanide is slightly more deeply colored than when the azide is not used, but still reveals the color of the underlying metal.

As an example of the use of sodium azide as a preliminary treatment, a piece of copper was dipped in a 2% solution of sodium azide for minutes. After washing it was dipped in a 1% solution of potassium ferrocyanide containing 0.1% of acetic acid for seconds. This sample withstood the previously described tarnish test for about 250 minutes. A similar sample showed good permanence in the well known weatherometer test in which it withstood more than two weeks exposure to moisture and strong light.

All of the many alloys containing over of copper that I have tested have an improved tarnish resistance after ferrocyanide treatment. Thus a brass containing of copper and 35% of zinc which will withstand the previously described tarnish test for about 60 minutes is untarnished after 200 minutes when given the ferrocyanide treatment, without having used the preliminary treatments mentioned.

It will be seen from the above that I have provided a novel method of treating copper or its alloys which is simple and comparatively inexpensive and which effectually protects such metals from tarnishing. Moreover, the method is such that the coating will reveal rather than conceal or obscure the natural beauty of the material treated. Likewise, the coating is of a smooth or horny texture with a consequent freedom from tendency to accumulate or retain dirt or other undesirable foreign matter. Obviously, my method is applicable to metals other than copper or its alloys.

It will further be understood that I have provided a method for the production of an article of manufacture which may take innumerable forms. One such form is illustrated in the accompanying drawing. In the drawing,

Figure 1 is a plan view. partly broken away,

of an article with my coating applied,

Figure 2 is asection taken on line 2-2 of Figure 1.

In the drawing, the copper or copper alloy is designated 1 and it will be seen that, as a result of my method, it has atransparent coating of a smooth or horny texture which is chemically combined with the copper or copper alloy and which efl'ectually serves to resist tarnishing thereof.

Having thus described my invention, what I claim is:

l. The method of treating copper or its alloys to prevent tarnishing which comprises treating it with a solution containing a soluble salt of hydroferrocyanic acid.

2. The method of treating copper or its alloys to prevent tarnishing which comprises treating it with a solution containing about 1% of a salt of hydroferrocyanic acid.

3. The method of treating copper or its alloys to prevent tarnishing which comprises treating it with a solution containing a salt of hydroferrocyanic acid and acetic acid.

4. The method of treating copper or its alloys to prevent tarnishing which comprises treating it with a solution containing a salt of hydroferrocyanic acid and about 0.1% of glacial acetic acid.

5. The method of treating copper or its alloys to prevent tarnishing which comprises subject- 'ing such metal to a solution of hypophosphorus acid and then treating it with a solution containing a salt of hydroferrocyanic acid.

6. The method of treating copper or its alloys to prevent tarnishing which comprises subjecting it to a solution containing an alkali salt of hydra zoic acid and then treating it with a solution containing a salt of hydroferrocyanic acid.

'7. The method of treating copper or its alloys to prevent tarnishing which comprises subjecting it to a solution containing about 2% of sodium azide and then treating it with a solution containing about 1% of potassium or sodium ferrocyanide and about 0.1% of acetic acid.

8. An article of manufacture comprising copper or copper alloy having a coating chemically formed .thereon bythe application of a soluble salt of hydroferrocyanic acid.

9. An article of manufacture comprising copper or copper alloy having a coating chemically formed thereon by the application of a salt of hydroferrocyanic acid and a dilute acid.

10. An article of manufacture comprising copper or copper alloy having a coating chemically formed thereon by subjecting it to a solution of hypophosphorus acid and then treating it with a solution containing a soluble salt of hydroferrocyanic acid.

11. An article of manufacture comprising copper or copper alloy having a coating chemically formed thereon by subjecting it to a solution containing a salt of hydrazoic acid and then treating it with a solution containing a soluble salt of hydroferrocyanic acid.

12. The method of treating copper or its alloys to prevent tarnishing which comprises treating itwith a solution containing a salt of hydroferrocyanic acid and a weak acid.

13. The method of treating copper or its alloys as a preliminary to the placing of a coating thereon by chemical combination therewith which comprises treating it with a solution of hypophosphorus acid.

14. The method of treating copper or its alloys as e. preliminary to the placing of a coating thereon by chemical composition therewith which comprises treating it with a salt of hydrazoic acid.

taining a salt of hydrazoic acid and then treating it with a solution containing hydroferrocyanic acid.

18. The method of treating copper or its alloys to prevent tarnishing which comprises subjecting the same to the action of a, solution capable of cleaning the copper surface and rendering it more receptive to the subsequent treatment and t then treating the said surface with a soluble salt of hydroferrocyanic acid in solution with a weak acid.

CLARENCE E. IRION. 

